Distortion

Vignetting

The vignetting characteristic seems to be a real weakness of Zeiss Z-series lenses when used on full format DSLRs.
The Distagon shows a fairly extreme deterioration of ~2.4EV at f/2 - this will be visible in most scenes. The
problem is still very pronounced at f/2.8 (@ ~1.4EV) but it's not overly significant anymore from f/4 onwards.

Here're some sample images from the lab:

f/2

f/2.8

MTF (resolution)

The Zeiss was able to deliver convincing results during our resolution tests. The center performance is great
straight from f/2 onwards. The borders/corners follow on a good to very good level here. The peak performance
is reached between f/4 and f/5.6 - the quality is very high across the frame here. Diffraction effects are
starting to have an impact from f/8 onwards. However, the quality is still easily usable at f/11.

Below is a simplified summary of the formal findings. The chart shows line widths
per picture height (LW/PH) which can be taken as a measure for sharpness.
If you want to know more about the MTF50 figures you may check out the corresponding
Imatest Explanations

Chromatic Aberrations (CAs)

Chromatic aberrations (color shadows at harsh contrast transitions) are comparatively low at around
1px on the average at the image borders. This may be visible at 100% magnification but it's not really
an issue on prints anymore.

Verdict

The Zeiss Distagon T* 35mm f/2 may not deliver superb results on full format DSLRs but the quality
is still impressive. The lens is sharp straight from f/2 and especially around f/4-5.6 and lateral CAs
are nothing to worry about either. The moderate degree of distortions is about average for a prime lens
in this class. However, a real weakness is the annoyingly high amount of vignetting at large aperture settings.
The quality of the bokeh is pretty good for a lens in this class (and easily superior to the EF 35mm f/2).

Just like the rest of its family the Zeiss lens is built to the highest standards. Some users may complain
about the lack of AF but this isn't really a significant flaw for a wide-angle lens. The focus confirmation
is available in the viewfinder (ZE version) and in very critical (close focus) scenes Live-View can give
you the needed guidance. That said, it remains a bit of an anachronism these days.
The price level is quite steep so you really have to have a itch for such classic lenses.